1. Field of the Invention
The present invention relates generally to electronic devices, and more particularly to digital camera modules. Even more particularly, the present invention relates to a system for focusing a digital camera module that prevents debris and particulate matter produced by the focusing process from contaminating the sensor array of an image capture device.
2. Description of the Background Art
Digital camera modules are currently being incorporated into a variety of electronic devices. Such camera hosting devices include, but are not limited to, cellular telephones, personal data assistants (PDAs), and computers. The demand for digital camera modules continues to grow as the ability to incorporate the camera modules into host devices expands. Therefore, one design goal of digital camera modules is to make them as small as possible so that they will fit into an electronic device without substantially increasing the overall size of the device. Furthermore, it is also desirable to manufacture such digital camera modules as efficiently and robustly as possible. Means for achieving these design goals must, of course, preserve the quality of the image captured by the camera modules.
FIG. 1 illustrates the basic components of a prior art digital camera module 100. Digital camera module 100 includes a lens unit 102 with a lens 103 contained therein, a housing 104, a substrate 106, and an image capture device 108. Substrate 106 is typically a printed circuit board (PCB) including electrical circuitry and contacts (not shown) of camera module 100. Image capture device 108 is mounted on and electrically coupled to PCB 106, and housing 104 is mounted on substrate 106 over image capture device 108. Lens unit 102 adjustably mounts to housing 104, by engaging a thread set 110 on lens unit 102 with a complementary thread set 112 in housing 104, so that an image can be focused onto image capture device 108 by lens unit 102.
Focal adjustment of lens unit 102 is facilitated by thread sets 110 and 112. During a factory focus operation, for example, focusing equipment rotates lens unit 102 with respect to housing 104, which adjusts the distance between lens 103 and image capture devices 108. When the lens unit 102 is properly focused, lens unit 102 is fixed in position with respect to housing 104 with an adhesive, a thermal weld, or the like.
Although camera modules that are focused via thread sets provide for relatively accurate focal adjustments, they suffer from several disadvantages. For example, threads are relatively difficult and expensive to manufacture on small optical components. In addition, small fine threads make screwing the lens unit into the housing a delicate operation. Furthermore, sliding friction between threads 110 of lens unit 102 and threads 112 of housing 104 creates particulate debris, which contaminate image capture device 108 or other imaging components of camera module 100 (e.g., infra-red filters, protective covers, other lenses, etc.). Such particulate debris noticeably degrades the quality of the captured images. Because digital camera modules are not easily disassembled and cleaned, particulate matter inside the module is particularly undesirable. It should also be noted that although threaded components are used here as an example, other types of focusing components located inside housing 104 can similarly produce particulate debris that reduces the quality of the captured images.
In efforts to minimize the costly process of manufacturing threaded camera modules, alternate focus features have been developed. For example, U.S. Pat. No. 6,426,839 issued to Dou et al. discloses a camera module including a plurality of ramps formed directly on a stationary lens located inside the camera module. A rotatable lens carrier (having a separate lens) includes a plurality of legs that engage the ramped surfaces of the stationary lens. Rotating the lens carrier causes the legs of the lens carrier to move up or down the ramped surfaces of the lens, thereby moving the second lens closer to or further from the stationary lens, depending on the direction of rotation. Although U.S. Pat. No. 6,426,839 may help reduce manufacturing cost, the focusing means are still located inside the camera module. Because the legs of the lens carrier slide over the ramped surfaces of the stationary lens, particulate debris can still be produced and collect on the imaging components of the camera module.
What is needed, therefore, is a camera module that can be manufactured inexpensively. What is also needed is a camera module that is easy to assemble. What is also needed is a camera module that minimizes contamination of the optical components during assembly and focusing.